The polyphenylene ether resins are an art-recognized class of engineering thermoplastics which are extrudable and moldable into articles of various shapes and sizes. Such polymers and methods for their preparation are described in the patent literature, including U.S. Pat. Nos. 3,306,874 and 3,306,875 (Hay), U.S. Pat. Nos. 3,257,357 and 3,257,358 (Stamatoff), and elsewhere.
Cizek in U.S. Pat. No. 3,383,435 discloses thermoplastic compositions of polyphenylene ether resin and styrene resin, including rubber modified styrene resin. The compositions can be shaped into articles having better properties than the polyphenylene ether resin alone.
Cooper in U.S. Pat. No. 3,960,985 describes thermoplastic compositions of a polyphenylene ether resin, an alkenyl aromatic resin and an organopolysiloxane. The compositions are described as having good thermal stability, resisting discoloration when processed at elevated temperatures.
Gowan in U.S. Pat. No. 3,361,851 discloses blends of a polyolefin and a polyphenylene oxide. As taught in the patent, the presence of the polyolefin improves the notched Izod impact strength and resistance to cracking upon exposure to aggressive solvents, while also acting as a plasticizer for the polyphenylene oxide.
Experience has shown that polyphenylene ether(oxide) resins are not readily compatible with all other polymers, and that, in fact, these resins will tolerate only relatively small amounts of some other polymers, such organopolysiloxanes or polyolefins, without detriment to physical properties. Thus, for instance, Gowan teaches in column 3, on lines 36-39 that up to about 10 percent by weight of a polyolefin can be incorporated into a polyphenylene oxide before incompatibility is noticed. Above 10 percent, the molded parts tend to delaminate and the composition begins to weaken.
Similarly, in practice it has been found that diorganopolysiloxanes are not fully compatible with polyphenylene oxide resins over the full range of relative amounts. Lovgren, et al. in U.S. Pat. No. 4,446,0190 disclose a procedure for blending a thermoplastic polymer, for example, a polyolefin or a polyphenylene ether, with a silicone fluid on a continuous basis. The thermoplastic is melted in an extruder, a high viscosity silicone fluid is injected directly into the melt, and the two are thereafter processed together through the remaining portion of the extruder.
Lovgren, et al. disclose in column 6, beginning on line 6, that these compositions can also include additives, for example, cross linking agents, among others, and that either the thermoplastic polymer or the silicone fluid may be preblended with the additive before the thermoplastic and silicone are mixed together in the extruder.